It is known that a gas that is compressed in a compressor element undergoes a substantial temperature increase.
For compressor devices with a number of stages, as referred to here, the compressed gas is supplied from a compressor element to a subsequent compressor element.
It is known that the compression efficiency of a multistage compressor is highly dependent on the temperature at the inlet of each compressor element of this multistage compressor and that the lower the inlet temperature of the compressor elements, the better the compression efficiency of the compressor.
That is why it is known to use intercoolers between two successive compressor elements to ensure maximum cooling and to obtain the highest possible compression efficiency.
It is also known to cool the compressed gas after the last compressor element before the gas is supplied to the consumer network because otherwise damage could occur to the consumers in the network on account of too high temperatures.
With the known compressor devices with a number of stages, the cooling, and more specifically the coolers, are generally attuned for maximum cooling for the purpose of maximum compression efficiency, whereby an available coolant, generally water, is driven from a cold source through the coolers in parallel so that each cooler receives coolant at the same cold temperature for maximum cooling.
Such a parallel supply of the coolers is highly suitable for optimum compression efficiency but requires a relatively high coolant flow rate for a sufficient supply of coolant to each cooler, which has the disadvantage that such a parallel supply is not optimum with regard to the required pumping power and size of the required cooling circuit and coolers.
Another disadvantage is that the flow rate of the coolant that flows through the coolers must be kept relatively high to bring about maximum cooling, such that the temperature of the coolant when leaving the compressor device is relatively low and as a result is poorly suited for recovering heat therefrom, for example in the form of the provision of hot water or similar.
Moreover, a high flow rate of the coolant also results in high investment costs, high operating costs and high maintenance costs of the cooling installation. Indeed, the heated coolant must be cooled in its turn in an air-water heat exchanger for example, whose dimensioning is highly dependent on the flow rate of the coolant and additives are also added to the cooling water to prevent limescale, counteract corrosion and inhibit bacterial growth.
For the purpose of better heat recovery it could be chosen to reduce the flow rate that is driven in parallel through the coolers and thereby increase the temperature of the coolant at the output, but this would be at the expense of the cooling and thus the compression efficiency.